1. Field of the Invention
The present invention relates to an antenna coil for use in a radio frequency identification (RFID) system that communicates with an external apparatus using an electromagnetic signal and to an antenna device including the antenna coil.
2. Description of the Related Art
In RFID systems, which are being increasingly used in recent years, a mobile electronic device (e.g., a mobile phone) and a reader/writer both have an antenna for information communications mounted therein and exchange data therebetween.
An antenna coil for use in a tag employing the RFID technique is disclosed in Japanese Unexamined Patent Application Publication No. 2002-252518. FIG. 1 is an illustration that shows an example structure of an antenna coil described in Japanese Unexamined Patent Application Publication No. 2002-252518. In this antenna coil 11, an electrical insulating film 13 including conductors 14 and 16 formed on its surfaces is bent such that a flat-shaped magnetic core member 12 is sandwiched, and the ends are connected to form a coil. The use of an electrical insulating film in such a way enables the antenna coil to have a structure that is thinner than that in which a conductor is wound around a magnetic core member.
However, if the antenna coil described in Japanese Unexamined Patent Application Publication No. 2002-252518 is embedded in a mobile phone while the main surface of the antenna coil is arranged so as to be parallel with the main surface of the mobile phone, because the coil axis of the coil is parallel with the main surface of the mobile phone and the main surface of the antenna coil has no portion for allowing an intrusion of magnetic flux, only magnetic flux from the side of the antenna coil will pass through the coil axis of the antenna coil. Therefore, in actuality, communications cannot be performed. In order to utilize the antenna coil described in Japanese Unexamined Patent Application Publication No. 2002-252518 in a mobile phone, it is necessary to arrange the antenna coil in a direction perpendicular to the main surface of the mobile phone. Such a structure cannot allow the antenna coil to be used as one that can be mounted on a circuit board, and a structure for embedding and an operation therefor are inevitably complicated.